SLD Event Display of a Z particle decaying to two quarks. An electron and positron travelling in opposite directions (perpendicular to this page) collided at the center of the detector and annihilated, creating a Z. The Z subsequently decayed to a quark and anti-quark, which then hadronized to form two jets of particles traveling in opposite directions. These are the two jets of green tracks seen in this projection.

Research supported by the Office of Science is making progress in the intense search for the Higgs boson, which may be the force that finally explains why some fundamental particles have mass, but others do not. Higgs is the last undiscovered component of the Standard Model, physicists' current theory of matter and the forces of nature. The model includes three families of particles called quarks and leptons; bosons carry forces between other particles. The Standard Model predicts a relationship between the masses of the Higgs boson, the W boson (which carries the "weak force"), and a particle called the top quark. Precise measurements of the properties of the top quark and W boson at Fermi National Accelerator Laboratory and the Zo at the Stanford Linear Accelerator Center in the 1990s significantly narrowed the predicted range for the mass of the Higgs boson. The SLAC experiments obtained what remains the most precise prediction of the mass of the Higgs, hinting that it should be light.

Scientific Impact: These experiments told scientists what mass range to seek in direct measurements of the Higgs boson; when the Higgs is found, comparisons of direct and indirect measurements will provide a strong test of the Standard Model. The results also suggest that the Higgs might be within reach of existing accelerators.

Social Impact: Research on subatomic particles answers questions about the constituents and history of the universe, extending human understanding of nature and contributing to improvements in science education. In addition, although basic research is by definition a search for new knowledge without regard to its practical implications, such work often contributes to technologies with commercial value; examples include computers, lasers, and cancer treatments.

Reference: "Improved Direct Measurement of Leptonic Couplings Asymmetries with Polarized Z Bosons," K. Abe et al. (The SLD Collaboration), Phys. Rev. Lett. 86, 1162, (2001).

URL: http://www-sldnt.slac.stanford.edu/alr/

Technical Contact: Dr. Martin Breidenbach, mib@slac.stanford.edu

Press Contact: Jeff Sherwood, DOE Office of Public Affairs, 202-586-5806

SC-Funding Office: Office of High Energy and Nuclear Physics